1. Field of the Invention
This invention pertains to fixed dental prosthetics, and more particularly, to devices for restoring dentulous spaces in the dentulous arch.
2. Prior Art
One of the most common problems faced in the field of dentistry is loss of teeth. Tooth loss may range in severity from one tooth to all teeth in the mouth. Missing teeth cause problems in speech, chewing, personal appearance, malocclusion, and the temporo-mandibular joint. When a limited number of teeth are missing the restorative options include replacement of the missing teeth with a prosthesis called a fixed partial denture (bridge).
Fixed partial dentures are usually fabricated in the following manner:
a. The teeth on both sides of the space caused by missing teeth are ground down (prepared). PA1 b. Impressions are made of these teeth and the space between them. PA1 c. A metal framework (retainer) is fabricated to fit over the prepared teeth (abutments) with a false tooth (pontic) between the retainers. PA1 d. Dental porcelain is fused to the metal framework to simulate the appearance and function of natural teeth. PA1 e. The bridge is permanently cemented onto the prepared teeth. (Dental Clinics of North America 1987, July; 333-346 and 505-528). PA1 a. When healthy teeth are prepared for bridges the teeth are more susceptible to decay if the bridge is faulty, or if the bridge becomes loose during function. PA1 b. This method of bridgework is expensive, precluding its use in certain socioeconomic groups. PA1 c. The procedure is time consuming, involving many hours of the dentist's time, and the patient must return several times. It may take several weeks to complete. PA1 d. The procedure usually involves injection of local anesthesia. PA1 e. Complications of tooth preparation may occur causing pulpal death and then endodontics or even tooth extraction. PA1 a. Regarding the preparation of teeth which leaves the teeth susceptible to decay, the present invention relies upon extremely minimal tooth preparation, which extends only into the enamel. The teeth are thus preserved, for the most part, in their natural anatomical form. The chance for increased rate of decay is thus obviated. PA1 b. The expensive standard method of fabricating fixed partial dentures, precluding its use in many people, is definitely an inadequate feature of that technique. The invention described herein is by far much less expensive for the patient. The technique will allow people with less available income to enjoy the benefits of fixed partial dentures. PA1 c. The invention described herein is far less time consuming to fabricate and insert than the standard methods. It is possible to complete the replacement of many teeth in just one day. The patient's time is saved and the dentist's time is saved. PA1 d. The standard procedures and many of those described in the Prior Art necessitate local anesthetic injections which are uncomfortable for the patient. This invasive procedure also may lead to injury to the patient or the dentist because of the sharpness of the needle. The proposed invention does not require local anesthetic thus precluding such injuries. PA1 e. There are complications associated with tooth preparation in the conventional manner, such as intense heat generated by the high speed dental drill, and inadvertent exposure of the nerve during drilling. Both of these complications are further time consuming, often painful, and expensive. The invention described herein, will not cause either of these complications, because this procedure does not involve extensive grinding of the teeth. PA1 f. The deficiencies in the resin-bonded retainer technique are also overcome with the mechanically retained fixed partial denture. In contrast to the resin-bonded retainer, the mechanically retained fixed partial denture may be used in patients with heavy occlusion, and on teeth with short clinical crowns. The structural concept of this invention which involves engaging the tooth from opposite sides (buccal and lingual) eliminates the need for a path of insertion and the tooth preparation attendant thereto. PA1 a. The aforementioned three part device can be pre-fabricated industrially, such that the individual sizes and shapes of the various teeth, which are to be replaced, are readily available. Mass production techniques are far superior, in this regard, to the current method of having the dental laboratory technician fabricate, in wax, the tooth forms, which are then cast in metal using the lost wax technique. The standard fabrication of tooth forms or the "wax up" is time consuming, and may take several minutes to complete. In the preferred embodiment the three part device is prefabricated in acrylic resin (wax, plastic or any number of materials suitable for burnout and casting using the usual and standard lost wax technique are acceptable) and need only be minimally adjusted before insertion into the edentulous space, followed by addition of the retentive elements, and then casting. It is also possible to pre-cast this device in metal industrially, and add the retentive elements with solder, which decreases laboratory time even more. Thus a savings of many dollars, per unit, is realized. PA1 b. Far more significant, in this regard, will be the time saved by the dentist. In the standard technique, the dentist must prepare the abutment teeth with a succession of burs, drilling, water spray and suction, to render the tooth in the correct form to accept the standard retainer. The tooth, thus prepared, must then be covered by a device known as the "provisional crown" to protect it from the oral environment. Additionally, the space between the teeth must be filled with an artificial tooth to prevent drifting of the teeth while the permanent bridge is fabricated. This is known as the "provisional bridge". The provisional crowns and bridges may require one half hour, or more to fabricate and cement upon the patient's teeth. The provisional prostheses often fall out, are uncomfortable, or unsightly, and may necessitate yet another visit to the dentist's office for correction. PA1 a. Single units of the assembled three part device are luted together prior to casting by combining all of the buccal elements to each other; and combining all of the lingual elements to each other. PA1 b. The incisal attachment elements are removed and cast separately. PA1 c. The combined buccal elements are removed and cast together thus forming multiple combined buccal elements. PA1 d. The combined lingual elements are removed and cast together thus forming multiple combined lingual elements. PA1 e. After casting in metal the device is reassembled into the form that was established prior to casting. PA1 d. The incisal attachment elements and their porcelain coverings are prepared singly, and inserted into their respective apertures.
This method, though usually successful, does not take into account certain circumstances that would dictate a more conservative approach. For example:
Several inventors have addressed these aforementioned problems. U.S. Pat. No. 4,556,388 to Hader discloses a method of fixing dental prostheses with pins and fitted sockets. This method is adaptable to many situations. However, it differs substantially from the devise described herein. The structural components are based upon a sleeve type mechanism, as opposed to retentive elements or the interlock principle.
Another disclosure which furnishes background information is U.S. Pat. No. 4,163,318 in the name of Tigani which discloses a method of restoring edentulous spaces by means of an adjustable device whose central mechanism is a screw. This screw extends arms which engage abutment teeth. This design is novel but does not resemble the invention described herein in all methods of structure or design.
A similar device, with the U.S. Pat. No. 4,431,415 awarded to the same inventor Tiqani, differs from Patent No. 4,163,318 in certain details, but is of the same basic mechanical principle and thus does not resemble in structure or concept the device described herein.
U.S. Pat. No. 3,422,534 to Bahm deviates from the conventional art in that the pontics are mounted upon a sleeve which embraces a bar suspended from the abutment teeth thus filling the space caused by the missing teeth. This design employs abutment teeth that have been prepared in the conventional manner, thus exposing those teeth to the same aforementioned detrimental consequences. The sleeve/bar apparatus serves indeed to support the pontics, but is very dissimilar in concept and design to the system of this invention.
An apparatus of U.S. Pat. No. 3,423,827 awarded to Bahm and Andrews employs similar technology to U.S. Pat. No. 3,422,534 in that the basic principle relates to a bar which supports the pontics. This device also differs conceptually from the invention described herein.
U.S. Pat. No. 4,744,757 to Adair et al. discloses a fixed partial denture which attempts to alleviate problems of error in the conventional art by utilizing crowns resting upon the abutment teeth which have male/female attachments connected to them. These attachments then are joined with a medium cured with visible light radiation. This system again relies upon substantial preparation of the abutment teeth with the attendant problems. The concept and design are very different from the invention described in this application.
U.S. Pat. No. 4,877,400 is based upon a bar extending between abutment teeth which supports a porcelain bridge. This design has laudable goals in terms of esthetics. However, the preparation of the teeth, with the aforementioned problems associated therewith, renders this design inadequate to prevent harmful sequelae to the abutment teeth. The structural design resembles, in no way, the invention described herein.
U.S. Pat. No. 4,950,162 awarded to Korber et al, also utilizes a longitudinal bar which extends between the abutment teeth. The framework can be adjustable and also depends upon substantial preparation of the abutment teeth. Thus the structural concept and design can be seen to be considerably different from the invention proposed herein.
U.S. Pat. No. 5,007,836 to Gayso discloses a method of replacing missing teeth with a groove lock system. There is some utility to this concept but it is limited by its application to replace only one tooth. There are many conceptual and structural differences between this invention and the one proposed herein. For example, there is a one-piece pontic suspended between two teeth, and there are no retentive elements in U.S. Pat. No. 5,007,836. These differences, among others, differentiates the Prior Art from the invention proposed herein.
The Related Art includes an entire class of dental restorations called the Resin-Bonded Retainers. These restorations are successful in limited applications, but there are serious inherent problems in their structural concepts that preclude usage in many applications. The resin-bonded retainers are not advisable in patients with heavy occlusion because of a tendency to dislodge; the resin-bonded retainers are contraindicated on teeth with short clinical crowns; and the teeth must often be prepared in an elaborate fashion to generate a path of insertion. (Dental Clinics of North America, April, 1985, pp. 393-402).
All of the techniques cited, and all those that this inventor is aware of, do not employ the central design concept of the invention described herein. That design concept is the three part device having an interlocking attachment which passes through two opposing and retaining elements simultaneously thus supporting the pontics between the abutment teeth. The Prior Art, and though successful in many instances, still leaves a large number of concerns yet to be adequately addressed. The invention described herein addresses those concerns in the following manner:
The invention described herein addresses several of the most important concerns regarding the deficiencies of the Prior Art. The device disclosed herein has a unique structural concept which embodies strength and a conservative approach. The invention enables missing teeth to be replaced painlessly and expeditiously with fixed partial prosthodontics.